Method of forming an air gap within a structure by exposing an ultraviolet sensitive material to ultraviolet radiation

ABSTRACT

An ultraviolet sensitive material may be formed within a semiconductor structure covered with a suitable hard mask. At an appropriate time, the underlying ultraviolet sensitive material may be exposed to ultraviolet radiation, causing the material to exhaust through the overlying hard mask. As a result, an air gap may be created having desirable characteristics as a dielectric.

BACKGROUND

This invention relates generally to the fabrication of integratedcircuits and, particularly, to the fabrication of integrated circuitswith extremely low dielectric constants.

Low dielectric constant materials are used as interlayer dielectrics insemiconductor devices to reduce the RC delay and improve deviceperformance. As device sizes continue to shrink, the dielectric constantof the material between metal lines must also decrease to maintain theimprovement. The eventual limit for dielectric constant is k=1, which isthe value for a vacuum. This can only be obtained by producing a voidspace between metal lines, equivalent to creating a so-called air gap.The air itself has a dielectric constant very near 1.

One major issue facing air gap technology is how to remove sacrificialmaterial to facilitate multi-layer structures. Plasmas may bedestructive to the metal lines. Wet etches have many problems includingcapillary forces that can break the lines apart, difficulty in removingmaterial from small features, and difficulty in removing the wet etchchemical once it has been introduced. Thermal decomposition presents achallenge in that the sacrificial material must remain stable duringhigh temperature fabrication steps, but then decompose rapidly attemperatures that will not destroy the rest of the device.

Thus, there is a need for better ways to form openings within integratedcircuits.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged cross-sectional view of one embodiment of thepresent invention;

FIG. 2 is an enlarged cross-sectional view at an early stage ofmanufacturing the embodiment as shown in FIG. 1 in accordance with oneembodiment of the present invention;

FIG. 3 is an enlarged cross-sectional view at a subsequent stage ofmanufacture in accordance with one embodiment of the present invention;

FIG. 4 is an enlarged cross-sectional view at a subsequent stage ofmanufacture in accordance with one embodiment of the present invention;

FIG. 5 is an enlarged cross-sectional view at a subsequent stage ofmanufacture in accordance with one embodiment of the present invention;

FIG. 6 is an enlarged cross-sectional view at a subsequent stage ofmanufacture in accordance with one embodiment of the present invention;

FIG. 7 is an enlarged cross-sectional view at a subsequent stage ofmanufacture in accordance with one embodiment of the present invention;

FIG. 8 is an enlarged cross-sectional view at a subsequent stage ofmanufacture in accordance with one embodiment of the present invention;and

FIG. 9 is an enlarged cross-sectional view at a subsequent stage ofmanufacture in accordance with one embodiment of the present invention;

DETAILED DESCRIPTION

Referring to FIG. 1, a multilevel integrated circuit device 10,according to one embodiment of the present invention, includes a firstlevel 12 that includes a substrate 100, an ultraviolet absorbing etchstop/diffusion layer 104, a via-level interlayer dielectric 105, openareas or air gaps 109, metal lines 102, and a hard mask 103.

A second layer 14 may include a via-level interlayer dielectric 105 a,an air gap 109 a, a metal line 102 a, and a hard mask 103 a. Of course,additional layers may be used in some embodiments of the presentinvention.

As indicated in FIG. 1, the air gaps 109, 109 a may be formed within thesemiconductor structure. These air gaps then provide a very lowdielectric constant close to or equal to one in some embodiments of thepresent invention. Thus, the air gaps 109 isolate between lines in thesame layer, reducing line-to-line capacitance and, therefore, cross-talkand RC delays.

The manufacture of the device 10, shown in FIG. 1, may begin with thelayer 12 as indicated in FIG. 2 in one embodiment. An ultravioletabsorbing etch stop/diffusion layer 104 may be formed on a semiconductorsubstrate 100. A via-level interlayer dielectric may be formed over theetch stop/diffusion layer 104. An ultraviolet sensitive sacrificialmaterial 101 may be formed on top of the dielectric 105. The material101 may be a polyketoester, polyketoamide, or any other material thatdecomposes readily upon exposure to ultraviolet light. For example, thematerial 101 may be polyketoester-polyphenylene orpolyketoamide-polyphenylene block copolymer.

Ultraviolet light decomposes polymers that contain certain ketonegroups. In one embodiment, the material 101 may include the ketonegroups incorporated into a cross-linked aromatic polymer to produce athermally stable material that is susceptible to degradation byultraviolet light. Additionally, oxygen may be used in combination withultraviolet light to aid decomposition through oxidation by O₂ or ozone.Ozone is a powerful oxidant that is formed when ultraviolet lightinteracts with O₂.

The hard mask 103 may be formed on top of the material 101. The hardmask 103 may be porous or non-porous. The resulting structure is thenpatterned and etched to form metal lines 102 as indicated in FIG. 2. Thestructure shown in FIG. 2 may be described as a dual damascene structurewhich forms the layer 12 of FIG. 1.

Moving to FIG. 3, the sacrificial material 101 is removed through thehard mask 103 by exposing the structure 12 to ultraviolet light. Thismay be done in the presence of O₂ in some embodiments. This results inthe formation of the air gaps 109. In some embodiments, the destabilizedmaterial 101 exhausts through the hard mask 103 which may be porous insome embodiments. In other embodiments, suitable openings may beprovided to exhaust the decomposed material.

Turning to FIG. 4, atop the layer 12 is the ultraviolet absorbing etchstop/diffusion barrier 104 a, the via-level interlayer dielectric 105 a,the ultraviolet sensitive sacrificial material 101, the hard mask 103 a,and the ultraviolet absorbing etch stop/diffusion layer 104 b that formthe upper layer 14 in accordance with one embodiment of the presentinvention. The light absorbing layer 104 b protects the sacrificialmaterial 101 during patterning of the upper layer 14.

As shown in FIG. 5, an opening 111 is patterned in the etchstop/diffusion layer 104 b. Then, the photoresist 106 is deposited,filling the trench 111 formed in the etch stop/diffusion layer 104 b.Next, the photoresist 106 is patterned and removed to form the trench108. As indicated at 110, some of the sacrificial material 101 isexposed to the ultraviolet light during photolithography. However, thematerial 110 will be removed completely during a subsequent trench etchanyway.

The hard mask 103 a is not light absorbing since sacrificial material101 would be removed through it in subsequent steps. The hard mask 103 aremains for mechanical support of upper layers. Through the impositionof the layers 105 a and 104 b, the region 110 is appropriately shaped tobe part of a larger area that must be entirely removed when an L-shapedmetal line 102 is formed through the material 101 and the layers 105 aand 104 b.

As shown in FIG. 6, the trench 108 is utilized to expose an additionalregion 117 which is then etched all the way down to the etchstop/diffusion barrier 104 a thereafter. The resulting trench 117 iscaused to extend through the hard mask 103 a through the exposed portion110, the layer 105 a, and stopping on the etch stop/diffusion barrier104 a. Next, the photoresist is removed. An etch is done which widensthe opening 117 just created by extending through the hard mask 103 aand the rest of the exposed material 110 stopping on the layer 104 a, asshown in FIG. 7. An etch is also done through the hard mask 104 a. Asshown in FIGS. 7 and 8, this creates an L-shaped opening for the metalline 102 a having a wider upper portion 118 and a narrower lower portion117.

Next, the metal 102 a is deposited to fill the opening portions 117 and118, overlying the top of the layer 103 a, as shown in FIG. 8. In oneembodiment, the metal may be copper. Thus, a barrier, seed, and coppermay be deposited in one embodiment of the present invention.

Referring to FIG. 9, following a chemical mechanical planarization, inaccordance with one embodiment of the present invention, the metal line102 a is formed generally having an upper surface coincident with theupper surface of the hard mask 103 a. Then, the sacrificial material 101is removed through the hard mask 103 a by exposing it to ultravioletlight to form the structure shown in FIG. 1.

In some embodiments of the present invention, the sacrificial materialsare more stable toward normal thermal processing in device fabricationthan those utilized in connection with thermally decomposing material.Plasma exposure to metal lines may be avoided. There are no issues fromwet etching such as capillary action and surface tension.

While the present invention has been described with respect to a limitednumber of embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover all such modifications and variations as fall within thetrue spirit and scope of this present invention.

What is claimed is:
 1. A method comprising: forming an ultravioletsensitive material within a semiconductor structure; exposing saidmaterial to ultraviolet radiation; and causing said material to beremoved through said structure.
 2. The method of claim 1 includingcovering said ultraviolet sensitive material with an overlaying layer.3. The method of claim 2 including covering said ultraviolet sensitivematerial with a hard mask.
 4. The method of claim 1 where causing saidmaterial to be removed through said structure includes covering saidmaterial with a porous layer and causing said material to pass as a gasthrough said porous layer.
 5. The method of claim 1 including forming aregion having a dielectric constant of approximately one.
 6. The methodof claim 5 including removing said material through said structure tocreate an enclosed air gap.
 7. The method of claim 6 including exposinga portion of said ultraviolet sensitive material that is not intended tobecome an air gap and removing said exposed material.
 8. The method ofclaim 7 including filling the region where the exposed material wasremoved with another material.
 9. The method of claim 1 includingforming a multi-layer structure, and removing ultraviolet sensitivematerial within each of said layers.
 10. The method of claim 8 includingremoving the ultraviolet sensitive material by exposing said material toultraviolet radiation and thereafter applying a subsequent layercontaining ultraviolet sensitive material and thereafter removing theultraviolet sensitive material from the subsequent layer.
 11. A methodcomprising: forming an ultraviolet sensitive material within asemiconductor structure; exposing said material to ultravioletradiation; enabling said material to be removed through said structure;and forming an air gap where said material exposed to ultravioletradiation was formed.
 12. The method of claim 11 including covering saidultraviolet material with an overlying layer.
 13. The method of claim 12including covering said ultraviolet sensitive material with a hard mask.14. The method of claim 11 wherein enabling said material to be removedthrough said structure includes covering said material with a porouslayer and enabling said material to pass as a gas through said porouslayer.
 15. The method of claim 11 including exposing a portion of saidultraviolet material that is not intended to become an air gap andremoving said exposed material.
 16. The method of claim 15 includingfilling the region where the exposed material was removed with anothermaterial.
 17. The method of claim 11 including forming a multi-layerstructure and removing ultraviolet sensitive material within each ofsaid layers.